1. Field of the Invention
The present invention relates to a coordinate measuring machine.
2. Description of Related Art
A coordinate measuring machine typically includes a probe having a measurement piece that is moved along a surface of an object to be measured, a moving mechanism that holds and moves the probe while scanning the surface and a controller for controlling the moving mechanism (see, for instance, Document 1: JP-A-2008-89578).
In such a coordinate measuring machine, a displacement of the moving mechanism is obtained to detect the position of the measurement piece, based on which a surface profile of the object and the like is measured.
However, since the moving mechanism is deformed on account of acceleration caused during the scanning movement of the probe, an error occurs between the obtained displacement of the moving mechanism and the position of the measurement piece, resulting in an error in the measurement value of the coordinate measuring machine.
Accordingly, in a surface profile measuring instrument (coordinate measuring machine) disclosed in the Document 1, an acceleration of the scanning movement of the probe is calculated based on a scanning vector (a command value for the scanning movement of the probe). Then, a correction-amount for correcting the position error of the measurement piece caused on account of the deformation of the driving mechanism (moving mechanism) is calculated based on the calculated acceleration.
Incidentally, in order to accept various profiles of objects to be measured, a multiple number of probes are exchangeably attached to such a typical coordinate measuring machine. Further, a probe that is rotated relative to the moving mechanism to change the attitude thereof has come to be recently used.
In the surface profile measuring instrument disclosed in Document 1, the correction amount for correcting the position error of the measurement piece is calculated based on the acceleration of the driving mechanism considering solely of the deformation of the driving mechanism. Accordingly, the same correction amount is calculated when, for instance, probes of different lengths are used or when the attitude of a probe is changed.
However, when probes of different lengths are used, the position of the measurement piece is altered even when the deformation of the moving mechanism is equal. When the attitude of the probe is changed, the position of the measurement piece relative to the driving mechanism is altered. Accordingly, the surface profile measuring instrument disclosed in the Document 1 fails to calculate an appropriate correction amount in the above circumstances, thus unable to properly correct an error in the measurement value.